1. Field of the Invention
The present invention generally relates to a mobile packet data communications system and, more particularly, to a method and apparatus for controlling asymmetric dynamic radio bearers in a mobile packet data communications system.
2. Discussion of Related Art
There have been developed and provided various services concerning data such as text, audio and video data in the recent new radio communications system, for example, PCS and IMT-2000, etc. Further, the system provides the data service at a fixed data rate in a bi-directional way.
The data rate is controlled by an MAC (Medium Access Control) provided in the individual apparatus.
Hereinafter, reference will be made in connection with the accompanying drawings as to a description of a mobile packet data communications system in accordance with prior art.
FIG. 1 is an illustrative diagram of a related art mobile packet data communications system, which includes a mobile station 1 requesting a radio data service and a network 2 providing the radio data service to the mobile station 1.
The mobile station 1 includes an MAC 1a for controlling transmit data according to the data rate corresponding to the requested radio data service and transmitting them through a transmit buffer 1b. 
The network 2 includes an MAC 2a for examining the data rate corresponding to the radio data service requested by the mobile station 1 and a transmit buffer 2b through which the radio data service is transmitted to the mobile station at the data rate.
Now, a detailed description will be made as to the operation of the related art mobile packet data communications system as constructed above.
First, when the MAC 1a of the mobile station 1 requests the network 2 to provide a specified data service, the MAC 2a of the network 2 examines a fixed data rate corresponding to the data service.
Upon examining the fixed data rate, the network 2 informs the mobile station 1 of the data rate to make a condition for the data service and providing the data service for the mobile station 1 with radio bearers for the data rate.
The radio bearers for the fixed data rate are controlled respectively by the MACs 1a and 2a to provide a symmetric data service communicated between the mobile station 1 and the network 2.
In such a related art mobile packet data communications system, the packet data are transmitted by using all the radio bearers at a fixed data rate since the data rate corresponding to the data service communicated between the mobile station and the network is fixed, thereby causing problems such as inefficient utility of the radio resources, excessive power consumption and signal interference.
Accordingly, it is an object of the present invention to provide a method and apparatus for controlling asymmetric dynamic radio bearers in a mobile packet data communications system in which the data rate can be varied by activating only a part of the radio bearers for a predetermined data rate according to the amount of data to be transmitted in a specified mobile data service.
To achieve the first object of the present invention, there is provided a method for controlling asymmetric dynamic radio bearers in a mobile packet data communications system including the steps of: (a) establishing a plurality of radio bearers having a predetermined data rate; (b) examining the amount of data stored in a transmit buffer during transmission of mobile packet data; and (c) transmitting the mobile packet data with the number of the radio bearers increased or decreased according to the amount of data.
In the step (c), the amount of data stored in the transmit buffer is compared with first and second thresholds THLOW and THHIGH, and the number of the radio bearers is decreased by one when the amount of data is lower than the first threshold THLOW and increased by one when the amount of data is higher than the second threshold THHIGH. And, the number of the radio bearers is not changed when the amount of data stored in the transmit buffer is kept between the first and second thresholds THLOW and THHIGH.
In the step (c), the number of the radio bearers is decreased by one when the amount of data stored in the transmit buffer keeps lower than the first threshold THLOW until a predetermined time expires and increased by one when the amount of data stored in the transmit buffer keeps higher than the second threshold THHIGH until the predetermined time expires.
The first and second thresholds THLOW and THHIGH are between hysteresis values for preventing frequent changes of the amount of data stored in the transmit buffer. The hysteresis values comprise first and second hysteresis values are opposite to each other with the first threshold THLOW interposed therebetween and separated from the first threshold THLOW at a predetermined distance, and third and fourth hysteresis values are opposite to each other with the second threshold THHIGH interposed therebetween and separated from the second threshold THHIGH at a predetermined distance.
The above steps are supported in MAC (Medium Access Control) protocols of a mobile station and a network.
Alternatively, there is provided a method for controlling asymmetric dynamic radio bearers in a mobile packet data communications system including the steps of (a) storing first and second thresholds THLOW and THHIGH; (b) establishing a plurality of radio bearers having a predetermined data rate; (c) comparing the amount of data stored in a transmit buffer with the first and second thresholds THLOW and THHIGH during transmission of mobile packet data; and (d) decreasing the number of the radio bearers by one when the amount of data is lower than the first threshold THLOW for a predetermined time and increasing the number of the radio bearers by one when the amount of data is higher than the second threshold THHIGH.
There is further provided an apparatus for controlling asymmetric dynamic radio bearers in a mobile packet data communications system including: a transmit buffer for temporarily storing transmit data according to a radio data service; and controlling means for establishing a plurality of radio bearers for transmission of the transmit data at a data rate corresponding to the radio data service, examining the amount of data stored in the transmit buffer and increasing or decreasing the number of the radio bearers.
The controlling means determines first and second thresholds for increasing or decreasing the number of the radio bearers. The first and second thresholds THLOW and THHIGH are between hysteresis values for preventing frequent changes of the amount of data stored in the transmit buffer. The hysteresis values include first and second hysteresis values are opposite to each other with the first threshold THLOW interposed therebetween and separated from the first threshold THLOW at a predetermined distance, and third and fourth hysteresis values are opposite to each other with the second threshold THHIGH interposed therebetween and separated from the second threshold THHIGH at a predetermined distance.